U.S. patent number 5,283,413 [Application Number 07/883,210] was granted by the patent office on 1994-02-01 for assembly process by welding of two solid copper pieces and assembly performed using such a process.
This patent grant is currently assigned to Merlin Gerin. Invention is credited to Jean-Paul Favre-Tissot.
United States Patent |
5,283,413 |
Favre-Tissot |
February 1, 1994 |
Assembly process by welding of two solid copper pieces and assembly
performed using such a process
Abstract
Two solid copper pieces are assembled by welding without filler
metal. The pieces both have a projection which are placed facing
and in contact with one another, before the pieces to be assembled
are placed on the welding press. Welding is performed by passing a
very high intensity current for a short period of about one tenth
of a second under very high pressure. The welding operation
prevents any annealing of the copper.
Inventors: |
Favre-Tissot; Jean-Paul
(Brignoud, FR) |
Assignee: |
Merlin Gerin
(FR)
|
Family
ID: |
9413119 |
Appl.
No.: |
07/883,210 |
Filed: |
May 14, 1992 |
Foreign Application Priority Data
|
|
|
|
|
May 21, 1991 [FR] |
|
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91 06306 |
|
Current U.S.
Class: |
219/93;
219/118 |
Current CPC
Class: |
B23K
11/18 (20130101); B23K 11/14 (20130101) |
Current International
Class: |
B23K
11/14 (20060101); B23K 11/18 (20060101); B23K
11/16 (20060101); B23K 011/18 () |
Field of
Search: |
;219/93,117.1,118 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
"Metals Handbook", vol. 6, Edition 9, Dec. 1983, pp. 503-524,
American Society for Metals. .
"Metals Handbook", vol. 6, Edition 9, Dec. 1983, pp. 548-556,
American Society for Metals. .
Welding & Metal Fabrications, vol. 55, No. 7, Oct. 1987, pp.
365-366, 368..
|
Primary Examiner: Evans; Geoffrey S.
Attorney, Agent or Firm: Parkhurst, Wendel & Rossi
Claims
I claim:
1. A process for welding first and second solid copper pieces
together without a filler metal, said first piece having front and
rear opposite major surfaces, comprising the steps of:
providing a first projection to extend from said rear surface of
said first piece and a first cavity opposite said first projection,
said first cavity extending into said front surface of said first
piece, said first cavity having a smaller cross-sectional width
than that of said first projection;
providing a first annular groove in said front surface of said
first piece to surround said first cavity, said first annular
groove having a depth less than that of said first cavity;
providing a second projection to extend from a surface of said
second piece;
arranging said first and second pieces such that said first and
second projections are in contact with each other;
applying a first electrode to said first piece upon said front
surface, said first electrode having a contact surface larger than
said annular groove such that said contact surface extends beyond
said annular groove and contacts a portion of said front surface
surrounding said annular groove;
applying a second electrode to said second piece, said first and
second electrodes being copper-based;
passing an electrical current between said first and second
electrodes through said first and second pieces and said first and
second projections to heat said first and second projections;
and
applying a compression force to the first and second pieces to
press said first and second pieces toward each other.
2. The process of claim 1, wherein said first and second
projections are semi-spherical to enable point contact
therebetween.
3. The process of claim 1, wherein said electrical current is
applied for about a tenth of a second, said electrical current is
about 100,000 amperes and said compression force is applied at a
pressure of a few hundred decanewtons.
4. The process of claim 1, wherein said second piece comprises
front and rear opposite major surfaces, said second projection
extending from said front surface of said second piece, wherein a
second cavity and a second annular groove surrounding said second
cavity are formed in said rear surface of said second piece, said
second cavity having a smaller cross-sectional width than that of
said second projection, said second annular groove having a depth
less than that of said second cavity, and wherein said second
electrode has a contacting surface larger than said second annular
groove such that said second electrode extends beyond said annular
groove and contacts a portion of said rear surface of said second
piece which surrounds said second annular groove.
5. The process of claim 1, wherein said first piece is
plate-shaped.
6. The process of claim 1, wherein said second electrode is a clamp
which radially grips the second piece so as to fixedly secure the
clamp to the second piece.
7. The process of claim 6, wherein said second piece is
cylindrical.
Description
BACKGROUND OF THE INVENTION
The invention relates to an assembly process by welding of first
and second solid copper pieces without filler metal.
In electrical switchgear a large number of solid pieces are made of
copper, whose good electrical conduction is well known. All the
assemblies of these solid copper pieces require hot joining by
brazing. The filler metal is generally a silver-based alloy whose
fusion point is lower than that of copper and the operation is a
delicate one. The copper is necessarily heated and it undergoes a
physical annealing transformation, and an external degradation due
to the carbon deposits from brazing. The pieces then have to be
cleaned and treated chemically to recover their original
appearance. The copper recovers part of its hardness with time.
SUMMARY OF THE INVENTION
The object of the present invention is to achieve assemblies of
solid copper pieces by means of a simple process, not using any
filler metal.
The assembly process according to the invention is characterized in
that it comprises the following steps:
shaping the first piece to form on its front face a projection and
on its rear face a conjugate cavity of smaller cross section than
that of the projection and an indentation in the shape of a ring of
limited depth surrounding the cavity,
shaping of the second piece to form a projection at an assembly
point to the first piece,
placing the first piece on a resistance welding press having first
and second copper-based electrodes, said front face facing the
second electrode, and the rear face being applied against the first
electrode whose cross section is greater than that of the
indentation and bears on the circumference of the indentation,
placing the second piece on the second electrode of the welding
press, the two projections being arranged in the axis of the press
and brought into point contact,
heating the two pieces by passing electrical current between the
first and second electrodes so that the current passes through the
first piece, via the two projections in contact with each other and
the second piece,
compressing of the two pieces by applying a pressure by the first
and/or second electrode to flatten the two projections and cause
welding.
The process is performed on a resistance welding press, heating of
the pieces being localized in the zone of the projections. The low
electrical resistance of copper makes it particularly difficult to
heat by passing current and therethrough. According to the
invention, this difficulty is overcome by a concentration of the
current flow in a limited zone, i.e. the contact point between the
two projections. The heating is thus localized in the zone of the
projections and causes fusion of the latter, which are deformed and
flattened by the pressure of the welding press to bring the two
pieces into contact. Welding of the two pieces is thus achieved
without any filler metal and without the risk of annealing or
tarnishing of the copper. The intensity of the welding current and
the welding pressure and current application time naturally depend
on the shapes and sizes of the pieces to be assembled. For example,
an assembly can be achieved between two copper current carrying
bars by passing a current of about 100,000 amperes for a very short
time, for example about one tenth of a second. The pieces are
subjected during the welding operation to a pressure of several
hundred decanewtons. The very short current passage time limits the
heat dispersion and heat rise of a notable part of the piece.
The second difficulty to be overcome is the heat rise of the
electrodes of the press and of the contact zone between the
electrodes and the piece. According to the invention, the
electrodes are copper-based, in particular cuprochrome, and
therefore have a low electrical resistance and reduced heat rise.
The heat rise in the contact zone is mastered by providing an
annular contact surface due to the ring-shaped indentation which is
arranged, according to the invention, around the cavity of the rear
face of the piece. The contact pressure is thus distributed
uniformally over an annular zone avoiding point contacts, which
cause heat rise and local welding. The diameter of the indentation
is for example about half the diameter of the electrode and its
depth is a few tenths of a millimeter.
The projection is advantageously in the form of a spherical cap
with a height of a few millimeters, and in the case of a piece in
the form of a bar or plate, it is advantageously achieved by a
stamping operation which results in a conjugate cavity on the
opposite face. The two pieces or plates to be assembled are placed
on one another and that their projections face each other and are
in contact before being inserted between the electrodes of the
press. The electrodes are then applied to the pieces with
insufficient pressure to notably deform the projections. This
deformation does however take place during the current passage
which causes a heat rise by resistance of the projections and local
fusion of the copper. The welding process according to the
invention is particularly well-suited for assembling bars or plates
which may have thicknesses of several centimeters, but it is
applicable to pieces of different shapes, notably revolution pieces
whose end has to be assembled to another piece, itself in the form
of a rod or in the form of a plate. The projection is then achieved
in any suitable manner, for example by simple machining, and the
electrodes of the welding press are adapted to the shape of this
piece by being arranged as a clamp having jaws for clamping the
piece for example. In this case, the clamping force of the piece by
the jaws is chosen to be sufficiently large to prevent any point
contact. This force is not exerted in the direction of the
projections and the risk of premature flattening of these
projections is therefore avoided.
The invention also relates to the welding press, enabling the above
process to be performed, and also to an assembly achieved by means
of this process .
BRIEF DESCRIPTION OF THE DRAWINGS
Other advantages and features will become more clearly apparent
from the following description of an illustrative embodiment of the
invention, given as a non-restrictive example only and represented
in the accompanying drawings, in which:
FIG. 1 is a schematic view of a welding press, the two pieces to be
assembled being inserted between the two electrodes before the
welding operation;
FIG. 2 is a cross-section on an enlarged scale of the two pieces
according to FIG. 1;
FIG. 3 is a view according to the line 3--3 of FIG. 2;
FIG. 4 is a similar view to that of FIG. 1 illustrating an
alternative embodiment;
FIG. 5 is a view according to the line 5--5 of FIG. 4.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the drawings a welding press 10 comprises a fixed lower
electrode 11 and a movable upper electrode 12, which can be moved
into contact with the lower electrode 11 by a mechanism which is
not shown. On the face 13 of the lower electrode 11 there is placed
a second piece 14 in the form of a bar, whose face opposite the one
placed on the electrode 11 bears a projection 15. A first piece to
be assembled 16 is placed on the second piece 14 and it also
presents a projection 17 which is pressed into contact with the
projection 15 of the opposite piece. The first piece 16 is also in
the form of a bar or plate and the only electrical contact between
the two pieces 14,16 is at the level of the projections 15,17. The
electrodes 11,12 are connected to a high intensity current source
18 and the welding operation is performed by closing of the
electrodes 11,12 and application of a strong pressure, for example
several hundred decanewtons. As soon as the press is closed, a high
intensity current is passed between the electrodes 11,12 and pieces
14,16 maintaining the pressure and it can easily be seen that the
current necessarily passes via the contact zone between the
projections 15,17 with a concentration in this zone which gives
rise to local heating and fusion of the metal forming the
projections. The duration is extremely short, for example a few
tenths of a second, which prevents any overheating of the pieces
14,16. As an example, it can be stated that two current input
strips in the form of bars can be assembled by providing a current
flow of 90,000 Amperes for a tenth of a second under a clamping
pressure of the pieces of 750 decanewtons. These values naturally
depend on the shape and thickness of the pieces 14,16.
The projections can be achieved by any suitable means, one of these
means being simple stamping of a piece in the form of a bar or
plate, which stamping results on the face opposite the projection
in a conjugate cavity 19 of a smaller cross section than that of
the projection 15,17. FIGS. 2 and 3 represent projections 15,17 in
the shape of a spherical cap made by stamping, but it is clear that
the shape of the projections 15,17 can be different, the only
obligation being an almost pin-point contact zone. Around each
cavity 19 there is arranged an indentation 25 in the form of a ring
of small depth, so that the electrode 11,12, whose cross section is
greater than that of the indentation 25, bears on the circumference
26 of the indentation 25 over a reduced distributed surface. The
diameter of the indentation 25 is greater than that of the
projection 15,17 and for example about half that of the electrode
11,12. The depth of the indentation 25 is small, for example a few
tenths of a millimeter.
FIGS. 4 and 5 illustrate an alternative embodiment enabling
assembly of a revolution piece 20 by its end 21 with a bar 16. The
length of the piece 20 prevents it from being inserted between the
two electrodes 11,12 of a standard press, and according to the
invention the lower electrode is arranged as a clamp having jaws 22
whose grips 23 are shaped to follow the revolution surface of the
piece 20. The end face 21 of the revolution piece 20 has a
projection 24 against which the projection 17 of the piece 16
presses. The welding operation is performed in the manner described
above and enables the bar 16 to be secured to the end of the
revolution piece 20. Assembly of pieces of different shapes is
naturally possible, the only obligation being a good electrical and
mechanical contact between the pieces and electrodes to prevent the
pieces from being welded onto the electrodes.
The invention is naturally applicable to copper-based pieces,
notably copper alloys, and the optimum welding parameters can
easily be selected by a crystallographic study of the weld. The
local heating of very short duration prevents annealing of the
copper which preserves all its mechanical properties, and the
absence of filler metal prevents any carbon deposits or other
impurities which might affect the qualities of electrical contact
with other pieces.
* * * * *